1. Field of the Invention
This invention relates generally to implantable medical devices, and more particularly, to a method and apparatus to automatically detect and monitor the frequency of obstructive sleep apnea.
2. Description of the Related Art
Although the function of sleep is not well understood, one consequence of an inadequate quantity or poor quality of sleep is an inability to maintain adequate wakefulness. The amount of sleep an individual needs is thought to be neurologically determined and is generally stable over time. Among other factors, an insufficient amount of sleep (i.e., quantity of sleep) or a disruption of sleep continuity (i.e., quality of sleep) will result in increased daytime sleepiness. Increased sleepiness in a person may cause a plethora of problems to that person as well as others. Increased sleepiness is a major cause of accidents because people who are sleepy are generally not fully aware of their surroundings. Additionally, because of this decreased awareness, a person who does not receive the adequate quantity and quality of sleep at night may also be prone to decreased efficiency at home and at work. A sleepy person may also require frequent naps during the day to recuperate, thereby reducing productivity in the office as well as in the chores of daily life. As a result, it is important for people generally to receive a good night's rest. However, many people have medical conditions that prevent them from receiving a good night's rest. One such condition is sleep apnea.
Sleep apnea is generally defined as the cessation of breathing during sleep. One type of a sleep apnea, obstructive sleep apnea (“OSA”), is caused by repetitive upper airway obstruction during sleep as a result of narrowing of the respiratory passages. Partial obstruction of the passageways may simply lead to hypopnea. Prolonged obstruction of the passageways, however, may lead to nocturnal arousals.
OSA is generally characterized by a sleep-related withdrawal of upper airway inspiratory muscle tone superimposed on a narrow, highly compliant pharynx. As a result, the pharynx may during sleep, leading to obstructive apnea.
The cause of OSA is thought to be a combination of anatomic characteristics of the upper airway and abnormalities in the neuromuscular control of the muscles in the throat. Sleep apnea is more common in individuals with large tonsils, palate, and tongue, and with a short thick neck. This anatomy may predispose the throat to easily collapse. A badly deviated nasal septum or other nasal obstruction can also worsen OSA because it limits the ability to breathe through the nose. Overweight individuals are also at high risk for OSA. Not all individuals with these anatomic features will have OSA, and OSA occasionally occurs in people with normal-appearing throats.
OSA may cause a variety of medical and other problems among patients. Cycles of sleep, snoring, obstruction, arousal, and sleep may occur many times throughout the night. Although such nocturnal arousals may last only a few seconds, they prevent a person from reaching the deep stages of sleep, which the body generally needs to rest and replenish its strength. As a result, patients with OSA may not receive a restful sleep because of multiple nocturnal arousals.
Furthermore, multiple arousals with sleep fragmentation are likely to cause excessive daytime sleepiness and fatigue, cognitive impairment, depression, headaches, chest pain, and diminished sexual drive. OSA is generally associated with cardiovascular morbidity, including systemic hypertension, pulmonary hypertension, ischemic heart disease, stroke, and cardiac arrhythmias. OSA is also usually associated with increased mortality by negatively affecting the status, progression, and outcomes of previously existing conditions, such as congestive heart failure (“CHF”).
OSA is a disorder which is generally underdiagnosed and undertreated. Because OSA may worsen the effects of a previously existing condition, such as CHF, treatment of OSA may be beneficial to reduce its negative on the previously existing condition. Once OSA has been properly diagnosed, a variety of therapies may be available. Common OSA therapies include non-surgical methods, such as continuous positive airway pressure (“CPAP”), as well as surgical methods, such as uvulopalatopharyngoplasty (“UPPP”). Effective therapy for OSA can often reverse or ameliorate the problems associated with OSA.
One method of diagnosis for OSA is nocturnal polysomnography. In nocturnal polysomnography, multiple physiological parameters are measured while the patient sleeps in a laboratory. Typical parameters in a nocturnal polysomnography include eye movement observations (to determine whether a patient has reached REM sleep), an electroencephalogram (to determine arousals from sleep), chest wall monitors (to document respiratory movements), nasal and oral air-flow measurements, and an electrocardiogram, among other parameters. A combination of these and other factors are used by doctors and other qualified sleep specialists to determine whether a patient has OSA. However, nocturnal polysomnography is generally expensive and time-consuming. Furthermore, many patients experience the symptoms of OSA (e.g., nocturnal arousals, snoring) while they are asleep, and therefore, never recognize that they may have a sleeping disorder. As a result, many patients with OSA may not seek proper diagnosis or treatment of their sleeping disorder from a doctor or other qualified sleep specialist. Even if a patient is diagnosed with OSA, frequent laboratory monitoring of the patient is generally not feasible due to the expense and time involved in a nocturnal polysomnography.
The technology explosion in the implantable medical devices industry has resulted in many new and innovative devices and methods for analyzing and improving the health of a patient. The class of implantable medical devices now includes pacemakers, implantable cardioverters, defibrillators, neural stimulators, and drug administering devices, among others. Today's state-of-the-art implantable medical devices are vastly more sophisticated and complex than early ones, capable of performing significantly more complex tasks. The therapeutic benefits of such devices have been well proven.
There are many implementations of implantable medical devices that provide data acquisition of important physiological data from a human body. Many implantable medical devices are used for cardiac monitoring and therapy. Often these devices comprise sensors that are placed in blood vessels and/or chambers of the heart. Often these devices are operatively coupled with implantable monitors and therapy delivery devices. For example, such cardiac systems include implantable heart monitors and therapy delivery devices, such as pacemakers, cardioverters, defibrillators, heart pumps, cardiomyostimulators, ischemia treatment devices, drug delivery devices, and other heart therapy devices. Most of these cardiac systems include electrodes for sensing and gain amplifiers for recording and/or driving sense event signals from the inter-cardiac or remote electrogram (“EGM”).
Many patients who use implantable medical devices may be at risk for OSA. However, patients are generally left with traditional forms of diagnosis for OSA, such as nocturnal polysomnography. As mentioned, nocturnal polysomnography may be an expensive and time-consuming procedure. Furthermore, many patients may not recognize that they have symptoms relating to OSA, such that they would seek diagnosis and treatment for the disorder. Nocturnal polysomnography is generally an infrequent procedure that does not provide long term monitoring of the patient's condition after he has been diagnosed. The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.